LIVE POLIO IRUS VACCINES

DISCUSSION
CHAIRMAN BURNET: The papers presented
by Dr. Pette and Dr. Hilleman are now open
for discussion.
DR. BARON: As regards the low isolation
rate of viruses from the central nervous system
of the monkeys inoculated with the attenuated
virus in Dr. Pette's study, we have had similar
experiences, that is, virulent strains resulted in
a very high isolation rate of virus, while the
avirulent strains gave a very low isolation rate,
approximating an over-all average of 30 per
cent.
On studying this further, and as we have reported
in the recent Federation Proceedings, an
inhibitory material was found in the central
nervous system of these suspensions of central
nervous system material as well as in CNS suspensions
from normal monkeys. This inhibitor
was able to inhibit one, two, sometimes three,
logs,, of virus. Upon dilution of some of the
originally negative central nervous system suspensions
from monkeys with poliovirus lesions,
we found that the virus was able to be isolated,
but not in all cases.
We are currently working on methods to destroy
the inhibitor selectively and leave the virus
intact. I think the point to be made is that
there may be a higher virus isolation rate once
the inhibitor in the central nervous system suspension
has been eliminated.
Are there further com-
CHAIRMAN BURNET:
ments? Dr. Gear.
DR. GEAR: As Dr. Hilleman has pointed out,
Dr. Malherbe, who is in charge of our safety
testing at the Poliomyelitis Research Foundation,
has taken a particular interest in the simian
viruses. These are now of increasing importance
and interest, and it may be recalled that
he and Harwin have described eight such viruses
in the South African vervet monkey, namely, SA
-which stands for simian agent, though perhaps
we should add South African in this particular
instance-SA-I, which is the foamy
agent; SA-II, which is the measles-like virus
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agent; SA-III, which is similar to, or identical
with ECHO-X virus; SA-IV and SA-V, both of
which produce changes somewhat similar to
those of the poliovirus but are not polioviruses;
SA-VI, which is a cytomegalic inclusion or
salivary-gland disease virus, presumably of
monkeys; SA-VII, an ECHO-like virus; and SA-
VIII, which is similar to the Herpes "B" virus.
In batches of vaccine, prepared recently from
Sabin's 'strain at the Laboratory of the Poliomyelitis
Research Foundation, it has been possible
to demonstrate the foamy agent in about
100 per cent of the batches prepared from five
or more monkeys, and in about 50 per cent of
kidneys from single monkeys.
Of some interest is the increasing proportion
of positive findings resulting from lengthening
the time of observation from three weeks to four,
and of subinoculating onto test tubes.
For example, in one particular batch, out of
12 bottles under test at three weeks, only one
showed the foamy agent. At four weeks, seven
showed the foamy agent; then, by subinoculating
onto tubes, an additional two were picked up.
In addition to the foamy agent, there have
been found several isolations of the measleslike
virus, and one can imagine that if we fed
measles virus on a large scale to fairly young
infants then there might be a severe epidemic of
measles.
Aside from the trouble with these agents, it
might be worth while to mention that in the
ECHO-XVI strains, which were received from
Dr. Sabin, another virus was isolated which we
have not isolated so far from South African
monkeys and which crosses with Hull's SV-VI
and Hull's SV-XVIII. Presumably, it was in
the original material.
In addition to the trouble with the monkey
kidneys, there has been similar trouble with
dog kidneys, most of which so far have contained
a virus which resembles distemper virus
in appearance. Even the young puppies we are
now using have had quite a proportion of this
virus.
One cannot assume, of course, that these
viruses are harmless. One would agree with